(a) Technical Field
The present invention relates to a system and method of controlling a fuel cell stack, and more particularly, to a system and method of controlling a fuel cell stack for recovering performance of the fuel cell stack.
(b) Background Art
Generally, a fuel cell vehicle is a vehicle that is powered by a fuel cell stack in which a plurality of fuel cells are stacked together to provide an appropriate amount in order to power the vehicle. These fuel cell systems typically include a fuel supplying system supplying hydrogen, (i.e., fuel or the like), to the fuel cell stack, an air supplying system supplying oxygen, (i.e., an oxidizing agent required for an electrochemical reaction), a water and heat managing system controlling a temperature of the fuel cell stack, and other components well known in the art.
The fuel supply system depressurizes the compressed hydrogen in a hydrogen tank and supplies the hydrogen to a fuel electrode (anode) of the fuel cell stack, and an air supply system supplies inhaled external air to an air electrode (cathode) of the fuel cell stack by operating an air blower.
When hydrogen is supplied to the fuel electrode of the fuel cell stack and oxygen is supplied to the air electrode thereof, hydrogen ions are separated through a catalytic reaction in the fuel electrode and the separated hydrogen ions are transferred to the air electrode as an oxidation electrode through electrolytic film. Here, the hydrogen ions separated from the fuel electrode, electrons and oxygen react together electro-chemically in the oxidation electrode to produce electricity. In more detail, hydrogen is electro-chemically oxidized in the fuel electrode and oxygen is electro-chemically reduced in the air electrode, electricity and heat are generated through the movements of electrons produced at that time, and water vapor or water is generated through a chemical reaction where hydrogen and oxygen are combined.
Meanwhile, an exhausting device is provided for discharging by-products such as water vapor, water and heat, which are produced while electricity is generated through the fuel cell stack, and non-reacted hydrogen, oxygen and the like. Gases such as water vapor, hydrogen, oxygen and the like are exhausted to the air through a discharging passage.
Here, configurations of an air blower, a hydrogen reflow blower, a water pump and the like for driving a fuel cell are coupled to a main bus terminal to easily turn on the fuel cell, and various relays for easily blocking and connecting electrical power and a diode to prevent reverse-current from flowing to the fuel cell may be connected to the main bus terminal.
Dry air supplied through an air blower is humidified through a humidifier and then is supplied to the cathode of a fuel cell stack, and the discharging gas from the cathode is transferred to a humidifier while it is humidified through water produced inside the fuel cell stack and may be used when humidifying the dry air to be supplied to the cathode by an air blower.
As is well known by those skilled in the art, fuel cell stacks are sensitive to the operation conditions such as external air temperature, cooling water temperature, current and the like and the state and performance thereof are determined based on these factors. As such, when a vehicle is continuously driven, especially in bad operation conditions, the performance of the fuel cell stack decreases and as a result reduces the output of the fuel cell stack. This affects the durability and deterioration of the fuel cell stack thereby shortening a life-span of the fuel cell stack in the long term.
Meanwhile, the dry out of the fuel cell stack is caused by two factors, one of which is caused at a high temperature output and the other of which is caused at a low output. The dry out at a high temperature output is caused when the heat balance inside the fuel cell stack is broken and the dry out at a low temperature is caused when the amount of water generation is reduced due to failed attempts to control the air supply and the optimal operating temperature, applying low current, and driving on free-load. Regardless, when the dry out of the fuel cell stack occurs, the output of the fuel cell stack is decreased and it takes long time to recover back to a normal output.
Furthermore, when the dry out of the fuel cell stack continues for a long time, the fuel cell system may not be able to recover due to unrecoverable performance reduction. Accordingly, the fuel cell stack needs to be controlled in manner that is able to sense promptly the situation where the fuel cell stack is in dry out state and operate the fuel cell stack to be recovered rapidly when the fuel cell stack is in a dry out state.
Further, even when the concentration of hydrogen is reduced due to its contamination when hydrogen is supplied as a fuel, the performance of the fuel cell stack may decrease. That is, when the output of the fuel cell stack is decreased, separate controls for the fuel cell stack due to the dry out and the hydrogen contamination are required.
The description provided above as a related art of the present invention is just for helping in understanding the background of the present invention and should not be construed as being included in the related art known by those skilled in the art.